X-ray analysis of samples is a growing area of interest across many industries such as medical, pharmaceutical, and petroleum. The use of x-ray fluorescence, x-ray diffraction, x-ray spectroscopy, x-ray imaging, and other x-ray analysis techniques has led to a profound increase in knowledge in virtually all scientific fields.
U.S. Pat. Nos. 6,934,359 and 7,072,439, incorporated by reference herein in their entirety and assigned to X-Ray Optical Systems, Inc., the assignee of the present invention, disclose monochromatic wavelength dispersive x-ray fluorescence (MWD XRF) techniques and systems for the analysis of liquid samples. Moreover, commonly assigned U.S. Pat. No. 7,277,527 (also included by reference in its entirety), entitled “Movable Transparent Barrier for X-Ray Analysis of a Pressurized Sample” addresses a particular problem inherent in moving sample streams as discussed further below.
X-ray fluorescence (XRF) is an analytical technique by which a substance is exposed to a beam of x-rays to determine, for example, the presence of certain components. In XRF, at least some of the chemical constituents of the substance exposed to x-rays can absorb x-ray photons and produce characteristic secondary fluorescence. These secondary x-rays are characteristic of the chemical constituents in the substance. Upon appropriate detection and analysis these secondary x-rays can be used to characterize one or more of the chemical constituents. XRF techniques have broad applications in many chemical and material science fields, including industrial, medical, semiconductor chip evaluation, petroleum, and forensics, among others.
As one particular example, these patents disclose techniques for the determination of the level of sulfur in petroleum fuels, and a commercialized analyzer (SINDIE) is now in widespread use for this measurement at petroleum refining, pipeline, and terminal facilities.
XRF techniques can be used for this application (as discussed above and throughout the above-incorporated patents). The basic technique involves exciting a fuel sample with x-rays and examining the fluorescence emitted. Each element emits a unique spectral signature. A detector then measures the wavelengths of the emitted x-rays, and software can reduce this measured spectrum to a weighted composition of the sulfur in the sample.
XRF fluid testing can take place off-line, i.e., using a bench-top, laboratory-type instrument to analyze a sample. The material is removed from its source (e.g., for fuel, from a refinery or transportation pipeline) and then simply deposited in a sample chamber; or into a windowed sample cell which is then deposited into a chamber. Off-line, bench-top instruments need not meet any unusual operational/pressure/environmental/size/weight/space/safety constraints, but merely need to provide the requisite measurement precision for a manually-placed sample. Moreover, off-line instruments can be easily maintained between measurements.
In contrast to off-line analysis, on-line analysis provides “real-time” monitoring of sample composition at various points in the manufacturing process. For example, all fuel products are subject to sulfur level compliance—requiring some variant of on-line monitoring during fuel refining and transportation in pipelines. On-line analysis of fuels in a refinery and in pipelines, however, requires consideration of numerous operational issues not generally present in an off-line, laboratory setting. A fully automated fuel sample handling system is required—with little or no manual intervention or maintenance. Also, since fluids are usually under pressure in pipelines, any sample handling system must account for pressure differentials. This is especially important since certain portions of XRF x-ray “engines” (discussed further below) operate in a vacuum. Also, the instrument's electronics require packaging in an explosion-proof housing—separate from the sample handling system.
In this application, therefore, one of the most critical components is the sample barrier(s) which allow photons of x-rays to excite sulfur atoms in the fluid, and photons emitted from the atoms to be counted at the engine's detector, while at the same time maintaining the vacuum in the x-ray engine and the pressure of the fluid. X-ray stimulation creates sulfur (or other hard element) ionization and adsorption at this interface over time and on certain types of barrier materials—leading to undesired sulfur residue and degradation of the barrier's x-ray transparency. More generally, many XRF applications require a barrier to protect the engine from any number of adverse interface effects from the sample material and/or the measurement environment.
The barrier system of above-incorporated U.S. Pat. No. 7,277,527, offered a very important and successful solution to these problems in the form of a moveable barrier advanced at programmable intervals to clean portions of a window roll. This technique, though successful and very functional in the field, has certain drawbacks, including the need to advance rolled, barrier material periodically using a mechanical system of rolls, motors, and controls. This barrier movement technique requires pressure adjustment, and moving parts to effect barrier movement. This barrier movement system itself requires periodic maintenance (and extra costs) to provide its function and also presents a potential failure mode in the system because of its complexity.
What is required, therefore, is a lower cost and lower maintenance barrier technique and apparatus for an on-line x-ray analysis system, which protects the x-ray engine from adverse sample and environmental effects, while maintaining the integrity transparency of the interface to the sample for accurate measurements without excessive moving parts.